Method for producing 1,2-benzisothiazol-3-ones

Abstract: A method for producing alkylthiobenzamide of formula (III) by carrying out a reaction of a halobenzamide with an alkanethiol in the presence of a base in a heterogeneous solvent; a method for producing an alkylsulfinylbenzamide by carrying out a reaction of an alkylthiobenzamide with a halogen in a heterogeneous solvent; a method for producing an alkylsulfinylbenzamide by carrying out a reaction of a halobenzamide with an alkanethiol in the presence of a base in a heterogeneous solvent and a subsequent reaction with a halogen; and a method for producing a 1,2-benzisothiazol-3-one of formula (VI) by carrying out a reaction of a 2-(alkylthio)benzamide with a halogenating agent.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a method for producing 1,2-benzisothiazol-3-ones. More particularly, the present invention relates to a method for producing 1,2-benzisothiazol-3-ones directly from 2-(alkylthio)benzamides. 1,2-benzisothiazol-3-ones are compounds useful as antibacterial agents and antifungal agents. Discussion of the Related Art There are several methods known for producing 1,2-benzisothiazol-3-ones, including the following ones. (C) Bull. Chem. Soc. Jpn., 55, 1183-1187 (1982) In the above method, 2-(methylthio)benzamide is produced from 2-(methylthio)benzoylchloride; oxidized with periodic acid to 2-(methylsulfinyl)benzamide; and cyclized in the presence of thionyl chloride to yield a 1,2-benzisothiazol-3-one. (D) Ger. Offen. 3500577 (1986) In the above method, a desired 1,2-benzisothiazol-3-one may be obtained using thiosalicylic acid as a starting material and sodium hydroxide as a cycling agent in the final process. (E) J. Org. Chem. 40(14), 2029-2032 (1975) In the above method, a desired 1,2-benzisothiazol-3-one is obtained using thiosalicylic acid as a starting material and a strong base in the final cyclization process. However, these conventional methods have the following drawbacks: In Method (C), a desired 1,2-benzisothiazol-3-one is synthesized in two steps, that is, 2-(methylthio)benzamide is oxidized to 2-(methylsulfinyl)benzamide, which is then cyclized in the presence of thionyl chloride. This method needs use of periodic acid, a dangerous and expensive substance. Method (D) requires expensive thiosalicylic acid as the starting material, a strong base for cyclization, and involves many reaction steps. Therefore, this method is not satisfactory for industrial use. Also, Method (E) uses expensive thiosalicylic acid as the starting material and a strong base for cyclization, and involves many reaction steps, and, therefore, is not suitable for industrial use. As stated above, all known methods require more than one reaction steps to produce 1,2-benzisothiazol-3-ones from 2-(alkylthio)benzamides, and are not satisfactory for production on an industrial scale. WO-A-94/20479 (published after the priority date of the present application) discloses N-(β-branched alkyl)-1,2-benzisothiazolin-3-ones having two or more carbon atoms in the alkyl side chain and processes for their production. The compounds are said to be useful as paint film fungicides. SUMMARY OF THE INVENTION Accordingly, in view of the above problems, an object of the present invention is to provide a method for producing 1,2-benzisothiazol-3-ones, important compounds as antibacterial agents, antifungal agents, etc., in high yield, by a safe and short process without using any expensive and dangerous substances. In order to achieve the object of the present invention, the inventors investigated the development of an industrially advantageous method for producing 1,2-benzisothiazol-3-ones. As a result, the inventors unexpectedly found that a 1,2-benzisothiazol-3-one represented by the general formula (VI) can directly be obtained by a reaction between a 2-(alkylthio)benzamide represented by the general formula (V) and certain halogenating agents. Unlike conventional methods, the cyclization can be achieved in one reaction step without proceeding via an intermediate alkylsulfinylbenzamide. The reaction can be represented as follows: wherein R 3 , R 4 and R 5 are as defined below. The present invention has been completed by conducting further research based upon the above findings. The present invention provides a method for producing a 1,2-benzisothiazol-3-one represented by the general formula (VI), comprising carrying out a reaction of a 2-(alkylthio)benzamide represented by the following general formula (V): wherein R 3 represents a hydrogen atom, or a linear or branched alkyl group having 1 to 12 carbon atoms, a cycloalkyl group, an aryl group selected from phenyl, 4-tolyl, 4-methoxyphenyl, 4-chloro phenyl and 1-naphthyl, or an aralkyl group selected from benzyl and phenethyl; R 4 represents an alkyl group having 1 to 4 carbon atoms; R 5 represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a nitro group, a carboxyl group or an ester thereof, or a halogen atom, with a halogenating agent selected from sulfuryl halides represented by the following general formula (VII): SO 2 X 2 wherein X represents Cl or Br, phosphorus pentachloride, phosphorus trichloride and chlorine, to give a 1,2-benzisothiazol-3-one represented by the following general formula (VI): wherein R 3 and R 5 are defined as above. According to the present invention, 1,2benzisothiazol-3-ones such as 2-phenyl-1,2-benzisothiazol3-one and 1,2-benzisothiazol-3-one, important substances as antibacterial and antifungal agents, can be produced from alkylthiobenzamides in high yield in one-step and under safe reaction conditions without use of expensive and hazardous substances. DETAILED DESCRIPTION OF THE INVENTION The method for producing a 1,2-benzisothiazol-3-one of the present invention employs a 2-(alkylthio)benzamide (V) as the starting material and the compounds of formula (V) are readily available for industrial use. The starting compounds cyclize in a single step to produce directly the 1,2-benzisothiazol-3-one (VI), unlike conventional methods which involve two-step processes via an intermediate alkylsulfinylbenzamide. Another feature of this method is that a 1,2-benzisothiazol-3-one can be produced safely under relatively mild conditions without using dangerous and expensive substances. The same definitions for R 3 and R 5 apply to both the formulas (V) and (VI). Specifically, R 3 represents a hydrogen atom, a linear or branched alkyl group having 1 to 12 carbon atoms, a cycloalkyl group, an aryl group or an aralkyl group. The alkyl groups for R 3 are exemplified by methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-decyl and n-dodecyl groups. The cycloalkyl groups for R 3 are exemplified by cyclopentyl and cyclohexyl. The aryl group for R 3 is selected from phenyl, 4-tolyl, 4-methoxyphenyl, 4-chlorophenyl and 1-naphthyl groups. The aralkyl group for R 3 is selected from benzyl and phenethyl. Preferred examples of R 3 include a hydrogen atom, and methyl, ethyl, isopropyl, n-butyl, tert-butyl, n-dodecyl, cyclohexyl, phenyl, 4-tolyl, 4-methoxyphenyl, 4-chlorophenyl, 1-naphthyl and benzyl groups, with a greater preference given to a hydrogen atom and a phenyl group. R 4 in the general formula (V) represents an alkyl group having 1 to 4 carbon atoms. The alkyl groups for R 4 are exemplified by methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl groups. Preferred examples of R 4 include methyl, ethyl, n-propyl and tert-butyl groups, with a greater preference given to methyl and tert-butyl groups. R 5 in the general formulas (V) and (VI) represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a nitro group, a carboxyl group or ester thereof, or a halogen atom. The alkyl groups for R 5 are exemplified by methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl groups. Alkoxy groups for R 5 are exemplified by methoxy, ethoxy, propoxy and butoxy groups. Esters of carboxyl group for R 5 are exemplified by methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl and butoxycarbonyl. Halogens for R 5 are exemplified by chlorine and bromine. Preferred examples for R 5 include a hydrogen atom, a n-butyl group, a methoxy group, a nitro group and a chlorine atom, with a greater preference given to a hydrogen atom. The starting materials, 2-(alkylthio)benzamides represented by the general formula (V) in the present invention are not particularly limited, and examples thereof include the following: 2-(methylthio)benzamide, 2-(ethylthio)benzamide, 2-(tert-butylthio)benzamide, N-ethyl-2-(methylthio)benzamide, N-ethyl-2-(ethylthio)benzamide, N-isopropyl-2-(methylthio)benzamide, N-(tert-butyl)-2-(methylthio)benzamide, N-hexyl-2-(methylthio)benzamide, N-octyl-2-(methylthio)benzamide, N-decyl-2-(methylthio)benzamide, N-dodecyl-2-(methylthio)benzamide, N-cyclohexyl-2-(methylthio)benzamide, N-phenyl-2-(methylthio)benzamide, N-(4-tolyl)-2-(methylthio)benzamide, N-(4-methoxyphenyl)-2-(methylthio)benzamide, N-(4-chlorophenyl)-2-(methylthio)benzamide, N-(l-naphthyl)-2-(methylthio)benzamide, N-benzyl-2-(methylthio)benzamide, N-benzyl-2-(propylthio)benzamide, N-benzyl-2-(butylthio)benzamide, N-phenyl-3-methyl-2-(methylthio)benzamide, N-methyl-5-butyl-2-(methylthio)benzamide, N-butyl-4-methoxy-2-(methylthio)benzamide, N-phenyl-2-methylthio-3-nitrobenzamide, 4-chloro-2-(methylthio)benzamide, 4-carboxy-2-(methylthio)benzamide, and 4-methoxycarbonyl-2-(methylthio)benzamide. Although a 2-(alkylthio)benzamide represented by the general formula (V) may be prepared by any methods, it can be obtained more advantageously by the method for producing an alkylthiobenzamide which forms the subject of EP-A-0 751 123 divided from the present application. The method for producing a 1,2-benzisothiazol-3-one from a 2-(alkylthio)benzamide of the present invention is carried out by the reaction of the 2-(alkylthio)benzamide with a halogenating agent. The detail of this method is hereinafter described. The halogenating agent is a sulfuryl halide [SO 2 X 2 (VII), wherein X represents Cl or Br], such as sulfuryl chloride or sulfuryl bromide, phosphorus pentachloride, phosphorus trichloride or chlorine. Among them, sulfuryl chloride, phosphorus pentachloride, phosphorus trichloride and chlorine are preferably used. The reaction solvents used for the halogenation process to obtain 1,2-benzisothiazol-3-ones are not particularly limited as long as they are inert to the reaction. Examples of suitable reaction solvents include hydrocarbons, such as n-hexane, n-heptane, cyclohexane, methylcyclohexane, benzene, toluene and xylene; and halogenated hydrocarbons, such as methylene chloride, 1,2-dichloroethane, chloroform, carbon tetrachloride, and monochlorobenzene. Of the above-mentioned reaction solvents, toluene, xylene and monochlorobenzene are preferred, because the entire process, i.e., from the synthesis of a 2-(alkylthio)benzamide represented by the general formula (V) by a reaction between a halobenzamide represented by the following general formula (VIII) and an alkanethiol represented by the following general formula (IX) to the synthesis of a 1,2-benzisothiazol-3-one by a reaction between the 2-(alkylthio)benzamide and a halogenating agent, can be very efficiently achieved in a one-pot: R 4 SH The conditions for the reaction between a halobenzamide (VIII) and an alkanethiol (IX) are as described in EP-A-0 751 123 referred to above divided from the present application. The amount of solvent used is normally 1 to 30 times the weight of 2-(alkylthio)benzamide used. The reaction temperature is normally 0 to 150°C, preferably 20 to 120°C. Reaction temperature higher than 150°C causes the problems of side reactions. On the other hand, reaction rate lowers to an impractical level when the reaction temperature is less than 0°C. The reaction time varies with the reaction temperature and the type of and reaction solvent, and it is normally in the range between 1 and 40 hours. A desired 1,2-benzisothiazol-3-one can be isolated and purified from the thus-obtained reaction mixture by the conventional methods, i.e., by distillation under reduced pressure when the desired 1,2-benzisothiazol-3-one is liquid, or by direct crystallization or extraction and subsequent recrystallization when the desired 1,2-benzisothiazol-3-one is solid. There is no limitation to these methods. Examples of 1,2-benzisothiazol-3-ones represented by the general formula (VI) obtained by the method of the present invention include: 1,2-benzisothiazol-3-one, 2-ethyl-1,2-benzisothiazol-3-one, 2-isopropyl-1,2-benzisothiazol-3-one, 2-(tert-butyl)-1,2-benzisothiazol-3-one, 2-hexyl-1,2-benzisothiazol-3-one, 2-octyl-1,2-benzisothiazol-3-one, 2-decyl-1,2-benzisothiazol-3-one, 2-dodecyl-1,2-benzisothiazol-3-one, 2-cyclohexyl-1,2-benzisothiazol-3-one, 2-phenyl-1,2-benzisothiazol-3-one, 2-(4-tolyl)-1,2-benzisothiazol-3-one, 2-(4-methoxyphenyl)-1,2-benzisothiazol-3-one, 2-(4-chlorophenyl)-l,2-benzisothiazol-3-one, 2-(l-naphthyl)-1,2-benzisothiazol-3-one, 2-benzyl-1,2-benzisothiazol-3-one, 7-methyl-2-phenyl-1,2-benzisothiazol-3-one, 5-butyl-2-methyl-1,2-benzisothiazol-3-one, 2-butyl-6-methoxy-1,2-benzisothiazol-3-one, 7-nitro-2-phenyl-1,2-benzisothiazol-3-one, 6-chloro-1,2-benzisothiazol-3-one, 6-carboxy-1,2-benzisothiazol-3-one, and 6-methoxycarbonyl-1,2-benzisothiazol-3-one. EXAMPLES The present invention will be further described by means of the following preparations and working examples. Incidentally, the product obtained in each case is examined by nuclear magnetic resonance ( 1 H-NMR) and mass spectroscopy in order to confirm that the desired product has been obtained. Preparation 1 Production of N-Phenyl-2-chlorobenzamide To a 500 ml four-necked flask equipped with a stirrer, a thermometer, and a condenser, 31.3 g (0.2 mol) of 2-chlorobenzoic acid and 180 g of toluene are placed. To the above mixture in the flask, 25.0 g (0.21 mol) of thionyl chloride is added dropwise over 30 minutes while stirring at a temperature of from 60 to 65°C to be allowed to react with each other for about 30 minutes. To the above reaction mixture, a solution containing 27.9 g (0.3 mol) of aniline dissolved in 100 g of toluene is dropwise added to be allowed to react with each other at a temperature of from 70 to 75°C for 30 minutes. After completion of the reaction, the reaction mixture is cooled to room temperature, and 70 g of a 5% by weight hydrochloric acid solution is added to the above mixture. The mixture is vigorously shaken and kept standing for separation of the toluene layer from the aqueous layer. After separation of the toluene layer, it is condensed to precipitate white crystals, followed by recrystallization (in a water/methanol mixture of 3/7), to give 43.1 g of N-phenyl-2-chlorobenzamide (melting point: 116 to 117°C). The yield of the product against 2-chlorobenzoic acid is 93%. Preparation 2 Production of N-Phenyl-2-(methylthio)benzamide To a 500 ml four-necked flask equipped with a stirrer, a thermometer, and a condenser, 46.3 g (0.2 mol) of N-phenyl-2-chlorobenzamide obtained in Preparation Example 1, 100 g of toluene, and 9.3 g of an aqueous solution of 50% by weight tetra-n-butylammonium bromide are placed. Separately, 12.0 g (0.30 mol) of sodium hydroxide and 113.7 g of water are placed into another container under a nitrogen gas atmosphere, and 14.5 g (0.30 mol) of methanethiol are added to the above mixture at room temperature over about 1 hour to prepare 140.2 g of sodium salt solution of methanethiol. 140.2 g (0.3 mol) of the aqueous solution of sodium methyl mercaptan thus prepared is added to the mixture containing N-phenyl-2-chlorobenzamide described above at 80°C while stirring, to be allowed to react with each other under reflux for 1 hour. After completion of the reaction, the reaction mixture is cooled to room temperature to precipitate white crystals, which are washed with water and then with toluene and dried, to give 46.2 g of N-phenyl-2-(methylthio)benzamide (melting point 148 to 149°C). The yield of the product against N-phenyl-2-chlorobenzamide is 95%. Example 1 Production of 2-Phenyl-1,2-benzisothiazol-3-one To a 500 ml four-necked flask equipped with a stirrer, a thermometer, and a condenser, 48.6 g (0.2 mol) of N-phenyl-2-(methylthio)benzamide and 100 g of toluene are placed. To the above mixture in the flask, 29.7 g (0.22 mol) of sulfuryl chloride is added while stirring at a temperature of from 20 to 30°C, and then the components are heated and allowed to react with each other at a temperature of from 70 to 80°C for 1 hour. After completion of the reaction, the reaction mixture is cooled to room temperature, and the precipitated white crystals are washed with toluene, and then dried to give 44.0 g of 2-phenyl-1,2-benzisothiazol-3-one (melting point: 140 to 141°C). The yield of the product is 97% against N-phenyl-2-(methylthio)benzamide, which is used as the starting material of the reaction. Example 2 Production of 1,2-Benzisothiazol-3-one To a 500 ml four-necked flask equipped with a stirrer, a thermometer, and a condenser, 33.4 g (0.2 mol) of 2-(methylthio)benzamide and 150 g of toluene are placed. To the above mixture in the flask, 28.3 g (0.21 mol) of sulfuryl chloride is added while stirring at a temperature of from 20 to 30°C, and then the components are heated and allowed to react with each other at a temperature of from 70 to 80°C for 1 hour. After completion of the reaction, the reaction mixture is cooled to room temperature, and the precipitated white crystals are washed with toluene, and then dried to give 29.0 g of 1,2-benzisothiazol-3-one (melting point: 157 to 158°C). The yield of the product is 96% against 2-(methylthio)benzamide, which is used as the starting material of the reaction. Examples 3 to 15 Production of 1,2-Benzisothiazol-3-ones The same procedures as in Example 1 are carried out except that N-phenyl-2-(methylthio)benzamide is replaced with each of the 2-(alkylthio)benzamides shown in Tables 1 to 3, to give a corresponding 1,2-benzisothiazol-3-one. In the case where the corresponding 1,2-benzisothiazol-3-one is a liquid, it is obtained by distillation under a reduced pressure. The melting points and the yields of the products are also shown in Tables 1 to 3. Example 16 Production of 2-Phenyl-1,2-benzisothiazol-3-one The same procedures as in Example 4 are carried out except that sulfuryl chloride in Example 4 is replaced with 83.4 g (0.4 mol) of phosphorus pentachloride, to give 36.7 g of 2-phenyl-1,2-benzisothiazol-3-one. The yield of the product against N-phenyl-2-(methylthio)benzamide is 81%. Example 17 Production of 2-Phenyl-1,2-benzisothiazol-3-one To a 500 ml four-necked flask equipped with a stirrer, a thermometer, and a condenser, 48.6 g (0.2 mol) of N-phenyl-2-(methylthio)benzamide prepared as in Preparation 2 and 100 g of monochlorobenzene are placed. To the above mixture in the flask, 18.5 g (0.26 mol) of chlorine is added while stirring at a temperature of from 40 to 50°C, and then the components are heated and allowed to react with each other at a temperature of from 70 to 80°C for 1 hour. After completion of the reaction, the reaction mixture is cooled to room temperature, and the precipitated white crystals are washed with monochlorobenzene, and then dried to give 44.5 g of 2-phenyl-1,2-benzisothiazol-3-one (melting point: 140 to 141°C). The yield of the product is 98% against N-phenyl-2-(methylthio)benzamide, which is used as the starting material of the reaction. Example 18 Production of 1,2-Benzisothiazol-3-one To a 500 ml four-necked flask equipped with a stirrer, a thermometer, and a condenser, 33.4 g (0.2 mol) of 2-(methylthio)benzamide and 150 g of monochlorobenzene are placed. To the above mixture in the flask, 18.5 g (0.26 mol) of chlorine is added while stirring at a temperature of from 40 to 50°C, and the components are then heated and allowed to react with each other at a temperature of from 70 to 80°C for 1 hour. After completion of the reaction, the reaction mixture is cooled to room temperature, and the precipitated white crystals are washed with monochlorobenzene, and then dried to give 29.3 g of 1,2-benzisothiazol-3-one (melting point: 157 to 158°C). The yield of the product is 97% against 2-(methylthio)benzamide, which is used as the starting material of the reaction. The results of Examples 1 to 18 are shown together in Tables 1 to 3.

Claims: A method for producing a 1,2-benzisothiazol-3-one represented by the general formula (VI), comprising reacting a 2-(alkylthio)benzamide represented by the following general formula (V): wherein R 3 represents a hydrogen atom, or a linear or branched alkyl group having 1 to 12 carbon atoms, a cycloalkyl group, an aryl group selected from phenyl, 4-tolyl, 4-methoxyphenyl, 4-chlorophenyl and 1-naphthyl, or an aralkyl group selected from benzyl and phenethyl; R 4 represents an alkyl group having 1 to 4 carbon atoms; R 5 represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, a nitro group, a carboxyl group or an ester thereof, or a halogen atom, with a halogenating agent selected from sulfuryl halides represented by the following general formula (VII): SO 2 X 2 wherein X is Cl or Br, phosphorus pentachloride, phosphorus trichloride and chlorine, to give a 1,2-benzisothiazol-3-one represented by the following general formula (VI): wherein R 3 and R 5 are defined as above. The method according to claim 1, wherein the compound represented by the general formula (V) is selected from: 2-(methylthio)benzamide, 2-(ethylthio)benzamide, 2-(tert-butylthio)benzamide, N-ethyl-2-(methylthio)benzamide, N-ethyl-2-(ethylthio)benzamide, N-isopropyl-2-(methylthio)benzamide, N-(tert-butyl)-2-(methylthio)benzamide, N-hexyl-2-(methylthio)benzamide, N-octyl-2-(methylthio)benzamide, N-decyl-2-(methylthio)benzamide, N-dodecyl-2-(methylthio)benzamide, N-cyclohexyl-2-(methylthio)benzamide, N-phenyl-2-(methylthio)benzamide, N-(4-tolyl)-2-(methylthio)benzamide, N-(4-methoxyphenyl)-2-(methylthio)benzamide, N-(4-chlorophenyl)-2-(methylthio)benzamide, N-(1-naphthyl)-2-(methylthio)benzamide, N-benzyl-2-(methylthio)benzamide, N-benzyl-2-(propylthio)benzamide, N-benzyl-2-(butylthio)benzamide, N-phenyl-3-methyl-2-(methylthio)benzamide, N-methyl-5-butyl-2-(methylthio)benzamide, N-butyl-4-methoxy-2-(methylthio)benzamide, N-phenyl-2-methylthio-3-nitrobenzamide, 4-chloro-2-(methylthio)benzamide, 4-carboxy-2-(methylthio)benzamide, and 4-methoxycarbonyl-2-(methylthio)benzamide. The method according to claim 1 or 2, wherein the 2-(alkylthio)benzamide represented by the general formula (V) is obtained by reacting a halobenzamide represented by the following general formula (VIII): wherein X represents Cl or Br; and R 3 and R 5 are as defined in claim 1, with an alkanethiol represented by the following general formula (IX): R 4 SH wherein R 4 is as defined in claim 1, in the presence of a base in a heterogeneous solvent.

Inventors: GODA HIROSHI, KOGANO HIROKAZU, SAKAUE SHIGEKI, GODA, HIROSHI, KOGANO, HIROKAZU, SAKAUE, SHIGEKI, GODA, HIROSHI, SUMITOMO SEIKA CHEM. CO., LTD., KOGANO, HIROKAZU, SUMITOMO SEIKA CHEM. CO., LTD., SAKAUE, SHIGEKI, SUMITOMO SEIKA CHEM. CO., LTD.
Applicants: SUMITOMO CHEMICAL CO, SUMITOMO SEIKA CHEMICALS, SUMITOMO CHEMICAL COMPANY, LIMITED, SUMITOMO SEIKA CHEMICALS CO., LTD.
Application year: 1994
Main classification: C07D257
IPC codes: C07D275, C07C323, C07C319, C07C317, C07C315